Fluid heater



FLUID HEATER Filed Deo. 4. 1929 2 Sheets-Sheet 1 INVENTORA ATTom/Ey.

March 3, 1931. w. H. ARMAcosT FLUID HEATER 2 Sheets-Sheet 2 Filed Dec.4, 1929 I N VEN TOR.

ATTRNEY.

Patented Mar. 3, 1931 UNITI-:D STATE-s PATENT `ol-Flcla e 'WILIB'UR H.ARMACOST, 0F NEW Y0RK,VN. Y., ASSIGNOR '.lO THE SUPERHEATER '.PANY, OFNEW YORK, N. Y.

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FLUID HEATER Application filed December 4, 1929, Serial No. 411,485, andin` Great Britain May 16, 1929.

My invention relates to fluid heaters and has particular reference toheaters of this type operating under extreme conditions of temperatureand pressure. The invention is particularly useful when incorporated inthe design of steam superheaters operating in conjunction with powerboilers, and this form of apparatus has therefore been chosen as theillustrative embodiment to be hereinafter described. It will beunderstood however, that the invention is not intended to be restrictedto use with superheaters, but is equally applicable to other comparableforms of heating apparatus.

This case is a continuation in part of United States application Serial`Number 346,279 filed on March 12,1929, and as to mattercommon to thatcase and the present one the filing date of the former is claimed forpurposes of priority.

The increasing use of higher operating pressures in modern power plantshas resulted in the production of steam having a high saturationtemperature, which, upon being superheated to the desired degree, mayattain a total. temperature of 800 deg. F. and over. In some instancessuperheated steam at temperatures considerably in excess of 800 deg. F.is required. In order to obtain steam temperatures of this magnitude, itis necessary to place the superheater in a zone of intense heat and theseverity ofthe service when the steam ltemperature is so high has madethe use of ordinary carbon steelv tubing impractical. It is a known factthat the heat transfer characteristics of asuperheater may be improvedby the use of very small diameter tubing, which operates to increase thevelocity of the steam through the superheater and to present a greaterarea of heating surface per unit volume of steaml With a superheaterconstructed of such small tubing, extreme conditionsA of pressure andtemperature could be withstood by ordinary'tubing, but such constructionisnot practically possible because of the excessive pressure droplentailed by the reduction in the size of the tubing to a diameter whichwill give otherwise satisfactory service. In order to meet thiscondition, tubing made of special alloy steels has beenemployed,particularly in the last pass lof the superheater, in which the steamconveyed therethrough is at or 'near its maximum temperature. tion,however, is extremely expensive and the principal object of the presentinvention is the provision of an improved form of superheater, by meansof which steam may be superheated to extreme temperatures and at highpressures without resorting to the use of expensive special materials. I

The invention has been illustrated as embodied in a superheaterinstalled in lan interdeck, cross-drum boiler of standard type,.although it is to beunderstood that the invention may equally well beapplied to superheaters in other locations in such boilers and inconjunction with other types of boilers. In .the drawings, Fig. 1 is asectional view showing the boiler and superheater arrange- `ment; Fig. 2is a fragmentary section illustrating a modified form of superheaterapplied in the same position as the superheater shown in Fig. 1; Fig. 3is a section on line 3--3 of Fig. 1; Fig. 3a is a section similar tothat of Fig. 3 illustrating a modification; and Fig. 4 is a section online 4-4 of Fig. 2; Figs. 3, 3a and 4 being on a considerably enlargedscale.

Referring now to Fig. 1, the boiler'comprises spaced banks or decks ofhorizontally inclined steam generating tubes 1 and 2 which are vfed from the Asteam and Water drum 3 through heaters 4 and 5, and theconnecting nipples 6 and 7. Headers 8 and 9, together with nipples l0and circulators 11, serve to connect the discharge end of tubes 1 and 2to the steam and water drum. Bailes 12 and 13 servev to direct thecombustion gases'over the tube banks in three passes in the usualmanner. n

The superheater is shown in the usual interdeck location in the spacebetween tube banks land 2 in the first pass, and comprises an inletheader 14 connected with the steannspace of drum 3 by means of pipe 15,van outlet header 16, and a plurality of tubular superheating units 17of the multi-loop type. The inlet portions of these superheater unitsare of thel diameter which would normally be This construcemployed, butadjacent to their outlet ends each unit is bifurcated as at '18 and theremainder of each unit comprises two tubes 17a and 17?) of smallerinside diameter connecting the bifurcation 18 with the outlet header 16.In the form shown it Will be noted that one loop of the four-loop unitvis made of the small tubing, but the relative lengths of the smalltubing and the large tubing will vary in accordance with the specificconditions for Which the individual super heater is designed. Also, therelation of the inside diameter of tubes 17 a and 17 b to the diameterof the major portion of the tubing 17 Will vary With individual designs.In some instances the increase Vin heat transfer eiiiciency due to theuse of the small tubing may be sufficient so that the combined sectionalarea of tubes 17 a and 17 b may be made equal to the sectional area oftube 17. In that case there is no increase in steam velocity through'thesmall-tube section as compared With the main portion of the unit and theonly increase in pressure drop Will be that due to the increase in thesurface area. In some instances it is possible that the increase in heattransfer eiiiciency due to the greater area per unit volume of thesmaller tubes Will permit the use of tubing of a size such that thecombined cross-sectional area of tubes 17 a and 17 b Will even begreater than that of tube 17, while in other instances it Will be neceslsary to provide an increase of steam velocity through the last pass bymaking the combined tube area smaller than the area of the tube 17. Inthe form illustrated'in Figs. 1 and 3 the sum of the inside areas of thetWo branches 17a and 17?) of the bifurcated part is the same as the areaof the single larger pipe, or approximately so. As will be readilyappreciated by those skilled in the art, the relative lengths anddiameters of the tubes 17ay and 17 b Will be determined by calculationin each individual case in order to provide a superheater which Willmeet the conditions of steam temperature and pressure drop imposed Whenemployed With the gas temperature, volume and velocity available. In thegreat majority of instances less than half the total area of heatingsurface Will be of the small diameter tubing, and it is generallydesirable to hold the proportion of heating surface formed of the smalltubing to a minimum in order to prevent undue pressure drop through thesuperheater.

In Figs. 2 and 4 a form of superheater is shown Which is particularlysuited for conditions vvhere an increase in steam velocity is required.In this form the superheated header 14 and the outlet header 16 areconnected by a plurality of multi-loop units 17. which instead of beingbifurcated near theiil outlet ends, as are the' units 17 shown in Fig.y

1, have their internal diameter reduced at approximately the same pointto provide a last pass or loop formed by a single small diametered tube1.70.

While any desired method of joining the large and small diameter pipestogether may be employed, the elimination of joints in high pressurepiping makes it desirable that the superheater units be made integral,and the bifurcated joint shown in Fig. 1 may convenientl be made by theprocess disclosed in U. S. Iratent No. 1,169,209 granted to C. H. True,et. al. on January 25, 1916, While the tubes 17 and 17C, shown in Fig.2, may conveniently be joined integrally through the medium of a forgedreturn bend manufactured by the process outlined in the above patent,supplemented by the process disclosed in Patent No. 1,255,355 issued toC. H. True, et al. on February 5, 1918.

From an inspection o-f Fig. 4 it will be noted that the Wall thicknessof the pipe 170 is greater than that of the pipe 17. In fact it isshown, and in practice' is preferably selected, such that the outsidediameters of the two are the same or substantially so. This thickeninghas the advantage of increasing the life of the pipe, and When the tWooutside diameters are the same it presents the furtherV` greatadvantage, when the unit is manufactured by the patented processmentio-ned, that it simplifies the manufacture and obviates thenecessity of special dies, which Would otherwise be required.

In installations in accordance with Figs. 1 and 3 the gauge of the tubesin the bifurcated part may evidently also be greater than that of thepipe in the single pipe part. This is illustrated in Fig. 3a.

The advantages accruin from the use of this invention may be brie ysummarized as follows: The major portion of the superheater units may bemade or ordinary carbon steeltubing of the size and thickness normallyemployed, as the temperature of the steam flowing through the firstportion of the units is sufficiently low to provide ample cooling forthem. Ordinary carbo-n steel may also be employed for the remainingportion of the units as the decreased diameter of the tubing used inthis portion of the units results in an increase in the heattransferiyefiiciency, by means of which the necessary cooling effect canbe obtained from the more highly superheated steam in this portion ofthe superheater. This increase in the heat transfer eiliciency, Whichresults in increasing the effectiveness of a given temperatured steam asa cooling agent, also permits the placing of the discharge end of thesuperheater units in a Zone of more intenseheat. Because of this factoritisv possible to arrange a superheater as shown in the accompanyingdrawings, so that eounterlow between the steam and the heating gases maybe employed.

Heretofore, when eXtreme conditions of temperature Were encountered, ithas been in tion of the gas path.

many cases necessary to forego the advantages of a counter-flowarrangement in order to obtain the cooling effect of the lowesttemperature steam in the .portion of the super-heater units located inthe hottest por- It will be clear that advantages need not be taken ofthis possibility of using the counter-flow arrangement, but that on thecontrary my invention is likewise advantageous when the flow of gasesand the flow of the stream are in the same general direction.

Because of the increased heat transfer efficiency of the smalldiametered tubes and the fact that the super-heater may be mostadvantageously arranged with respect lto the gas flow, a considerablereduction in the total amount of heating surface necessary to produce agiven degree of superheat may be ob- .1- tained. This results not onlyin a saving of superheater material, but also in many instances resultsin a substantial saving because of the more compact boiler arrangementpossible with the smaller superheater.

Vhile in accordance with the patent statutes I have described preferredforms of my invention, it is to be understood that they are illustrativeonly and that the invention embraces all such forms of apparatus as mayfall Within the scope of the appended claims. I claim:

1. In apparatus of the class described, the

pass, each of said units comprising an inletl portion Jformed of asingle tube and an outlet portion serially connected therewith formed ofa single tube of the same external but smaller internal diameter thansaid inlet tube.

3. In apparatus of the class described, the combination with meansdefining a pass for Y combustion gases, of a plurality of multi-looptubular heating units disposed generally transversely of the gas flowthrough the pass, each of said units being formed with at least the lastloop thereof composed of tubing having an internal diameter less thanthe internal diameter of the remaining loops and having a greater ywallthickness than the remaining loops.

4. Apparatus of the class described comprising an inlet header, anoutlet header, and a plurality of integral tubular heating unitsconnecting said headers, each of said units comprising a singlebifurcated tube connected at one end to the inlet header and a pair oftubes of smaller diameter than said single tube connecting thebifurcation with said outlet header, the cross-sectional area of saidsingle tube being at least as great as the combined cross-sectionalareas of said pair of' tubes.

V5. A superheater unit comprising an inlet portion formed by a tubebifurcated at one end and an outlet portion formed by a pair of tubesjoinedto the bifurcated end of said first named tube, the combinedcrosssectional area of said small diametered pipe being less than thecross-sectional area of said bifurcated pipe.

6. Apparatus of the class described comprising an inlet header, anoutlet header, and a plurality ofintegral tubular heatingunitsconnecting said headers, each of said units comprising a singlebifurcated tube connected at one end to the inlet header and a pair oftubes ot' smaller diameter but greater wall thickness than said singletube connecting the bifurcation with said outlet header, thecross-sectional area of said single tube being at least as great as thecombined cross-sectional areas of said pair of tubes.

7. The combination with a boiler having a bank of horizontally inclinedsteam-generating tubes and a baffle defining a transverse gas pass oversaid tubes, of a superheater located in said pass above said tube bank,said superheater comprising a plurality of multiloop tubular unitsdisposed generallytransverselyof the gas flow, each unit comprising aninlet portion formed by a single tube and an outlet portion comprising atube having a smaller diameter but a greater wall thickness than saidfirst named tubes and serially connected therewith.

WILBUR H. ARMACOST.

